C4 pathway

Definition

The C4 pathway is a specialized method of carbon fixation used by certain plants to efficiently capture carbon dioxide during photosynthesis. This pathway minimizes photorespiration and enhances photosynthetic efficiency, particularly in environments with high temperatures and low carbon dioxide concentrations. It is an adaptation that allows plants to thrive in hot and arid conditions, linking closely with the CAM pathway for additional efficiency.

5 Must Know Facts For Your Next Test

1. The C4 pathway involves two types of cells: mesophyll cells and bundle sheath cells, allowing efficient separation of the initial carbon fixation from the Calvin cycle.
2. In the C4 pathway, carbon dioxide is first fixed into a 4-carbon compound (oxaloacetate), which is then converted into malate before entering the bundle sheath cells for further processing.
3. This pathway is found in plants such as sugarcane, corn, and certain grasses, which are often referred to as C4 plants due to their specific adaptations.
4. C4 plants can achieve higher rates of photosynthesis than C3 plants under high light intensity and elevated temperatures, making them more competitive in certain environments.
5. The evolution of the C4 pathway has occurred independently in various plant lineages, demonstrating its significance as an adaptive strategy for coping with environmental stressors.

Review Questions

• How does the structure of C4 plants facilitate efficient carbon fixation compared to C3 plants?
  • C4 plants have a unique leaf structure that includes mesophyll and bundle sheath cells, allowing them to spatially separate the initial carbon fixation from the Calvin cycle. In mesophyll cells, carbon dioxide is first fixed into a 4-carbon compound, which is then transported to bundle sheath cells where it enters the Calvin cycle. This separation reduces photorespiration, leading to more efficient use of sunlight and water compared to C3 plants.
• Discuss the advantages of the C4 pathway in relation to environmental conditions that affect photosynthesis.
  • The C4 pathway provides significant advantages in hot and dry environments by minimizing photorespiration and maximizing photosynthetic efficiency. By fixing carbon dioxide into a 4-carbon compound at night or during cooler parts of the day, C4 plants can maintain higher rates of photosynthesis even when stomata are closed to prevent water loss. This adaptation allows them to thrive where C3 plants may struggle due to heat and limited water availability.
• Evaluate the evolutionary significance of the C4 pathway and its impact on plant diversity and ecosystem functioning.
  • The evolutionary significance of the C4 pathway lies in its independent development across various plant lineages as a response to environmental stressors like drought and high temperatures. This has led to increased plant diversity as species adapt to different climates, allowing C4 plants to occupy ecological niches that were previously dominated by less efficient C3 species. The presence of C4 plants can influence ecosystem functioning by enhancing primary productivity, altering nutrient cycling, and providing habitat for various organisms in those environments.

Related terms

Photorespiration:

A process that occurs when the enzyme RuBisCO reacts with oxygen instead of carbon dioxide, leading to a decrease in photosynthetic efficiency.

CAM pathway:

The Crassulacean Acid Metabolism (CAM) pathway is another adaptation for carbon fixation, where stomata open at night to minimize water loss, allowing plants to store carbon dioxide as organic acids.

Mesophyll cells: The cells in leaves where photosynthesis occurs, playing a key role in the C4 pathway by initially capturing carbon dioxide.